The present invention relates to an arrangement for multispectral imaging of objects, preferably targets. More specifically, the present invention relates to such an arrangement, particularly an infra-red (IR) sensitive or visible light sensitive search, detection or identification instrument or system employing an optical system which images the object dots of the objects on at least one charge coupled semiconductor element which includes a plurality of light sensitive indidivual detectors and a charge-transfer circuit arrangement.
Charge-coupled semiconductor detector devices for optical signals are generally known. They permit a transfer of charges in a controlled manner from one electrode to the adjacent electrode of a semiconductor substrate. They are able to perform an astonishingly broad range of electronic functions and are used, for example, as image sensors in television cameras or in videotelegraph systems.
Charge-coupled image sensors are divided into single-dimension sensors and area or surface sensors. Single-dimension sensors constitute a single straight line array of photosensors with combined read output and sensor circuit, the so-called charge transfer circuit arrangement. Area sensors have a two-dimensional mosaic of photosensors with a combined read output and sensor circuit. A charge transfer circuit includes two types of registers, namely, on the one hand, one serial register at its input and one at its output, each operated serially with two phases of a clock pulse and, on the other hand, parallel registers arranged between these serial registers to be operated in the multiplex mode.
Arrangements for imaging two-dimensional images with the aid of a linear charge-coupled image sensor are generally known in one known arrangement (Scientific American, February 1974, page 10) the image to be scanned is disposed on a rotating drum whose rate of rotation is synchronized, for example, with the vertical scanning phase of a display monitor. Thus, for example, the charge-coupled member and the series connected read-out circuit generate horizontal video lines at a clock pulse rate which is fast enough to display a complete section of a picture of the scene on the monitor.
To be able to make a distinction between two or more objects, particularly targets, in front of a structured background, it is known to compile signals from at least two wavelength ranges with the aid of individual detectors. A first portion of these individual detectors absorbs a first wavelength range while a second portion of the individual dectors absorbs another wavelength range. The drawback is that two separate channels are used with corresponding detectors. This arrangement employs a known arrangement with charge transfer. In another solution, the individual detectors which, in a disadvantageous manner, are arranged one above the other and are thus not simultaneously in the focal plane of an optical system, furnish electrical signals corresponding to the wavelength range absorbed by them to an evaluation circuit arrangement. However, in this arrangement no charge transfer circuit arrangement is possible.